4. Morrison's Plastics Division, 21 profit center, sells its products to external customers as \"mall as to other internal prot centers. W'hich one of the following circumstances would justify the Plastics Division selling a product internally to another prot center at a price that is below the marketbased transfer price? a. The buying unit has excess capacity. b. The selling unit is operating at full capacity. c. Routine sales commissions and collection costs would be avoided. d. The prot centers' managers are evaluated on the basis of unit operating income